I'm just avoiding claims without evidence... unlike the guy who says that SCGI is slow ;)
Other than that I guess it's useful if you want to display data from a C / C++ program without going through any bindings. When it comes to that, maybe it would be great to get some automatic HTML display helpers for data structures common in C, like Arrays of numerical values or pointers to sequences of structs. For example in Python it's really fun to just use something like [1] together with Flask and get interfaces to your data without doing any template programming.